1. Field of the Invention
The present invention relates generally to a pressure swing adsorption dryer for a pneumatically driven pressure intensifier. More specifically, the present invention relates to a pressure intensifier used in a pressure swing adsorption system. The present invention also relates to a kit for retrofitting existing pneumatically driven pressure intensifiers.
2. Description of the Related Art
The use of concentrators of the pressure swing adsorber type to produce an enriched product gas is well known. Pressurized air is cyclically delivered to a plurality of beds of molecular sieve material and certain components of the air become adsorbed by the sieve while the chosen component passes through. The beds are sequentially vented to atmosphere and purged with product gas to discharge the adsorbed components from the molecular sieve, and in this manner, a continuous flow of enriched product gas can be generated.
In certain situations, the required pressure of the product gas is higher than the output pressure from the adsorber and a pressure booster may be used to increase the pressure of the product gas in order to meet system requirements. Booster compressors themselves are old in the art and may take several forms. Some are electrically driven but in certain situations a pneumatically driven booster provides advantages. The pneumatic booster may be driven in sync with the beds of the pressure swing adsorber and such a system is shown in U.S. Pat. No. 5,071,453 assigned to the assignee of the instant invention.
The pneumatically driven pressure intensifier utilizes low pressure drive air acting on a large piston to shuttle smaller pistons which in turn compress product gas to an elevated pressure. In addition, in some cases, the compressor size can be minimized by using air conservation techniques as described in U.S. Pat. No. 5,354,361, the disclosure of which is hereby incorporated by reference into the present specification in its entirety. The drive gas is separated from the product gas through a series of shaft and piston seals, which allow the pistons and drive shaft to move while providing pneumatic integrity. The drive air used to shuttle the pistons contains water vapor which can condense in the drive cylinder. The presence of water in the drive cylinder can have serious detrimental effects on the performance of the pressure intensifier.
It is an object of the present invention to provide a drying apparatus for use with a pressure intensifier for drying drive gas before the drive gas enters the pressure intensifier.
It is another object of the present invention to provide two activated beds and one or more valves between a pressurized air source and a pressure intensifier for drying drive gas before it enters the pressure intensifier.
Another object of the present invention is to provide a retrofit kit for retrofitting existing pressure swing adsorption systems with a drying apparatus for drying drive gas before the drive gas enters the pressure intensifier.
It is still another object of the present invention to provide a pressure swing adsorber and a pneumatically driven booster in which the timing of the valves which control the operation of the concentrator and the booster, and the plumbing between the concentrator and the booster are selected to control the timing of the transfer of gases which are admitted to the sieve beds.
These and other objects of the present invention are achieved by a drying apparatus for a pressure swing adsorption system including a pair of beds having molecular sieve material with each bed having an inlet and an outlet. A pressure intensifier increases the pressure of enriched product gas. The pressure intensifier includes a pneumatic drive cylinder which has opposed sides which are alternatively pressurized in order to drive the pressure intensifier. The pair of beds and the pneumatic drive cylinder are coupled to a source of compressed feed air. The drying apparatus includes a pair of moisture removing beds each connected to the source of compressed feed air. At least one valve is located between the source of compressed feed air and the pair of moisture removing beds. The pressure intensifier is alternatively pressurized with feed air via the pair of moisture removing beds.
The foregoing and other objects of the present invention are achieved by a method of drying gas used in a pneumatically driven pressure intensifier. The pressure intensifier is used in a pressure swing adsorption system. The pressure swing adsorption system includes a pair of molecular sieve beds each connected to a first and a second valve, respectively. The first and the second valves are each connected to a source of pressurized gas and an ambient vent line. The method comprises flowing pressurized gas to opposite sides of the pressure intensifier drive cylinder to position the pressure intensifier drive piston. Pressurized gas flows through a first activated bed to dry the gas and to pressurize one side of the pressure intensifier drive cylinder to shift the pressure intensifier to a first position. Gas is vented from the other side of the pressure intensifier drive cylinder through a second activated bed which desorbs moisture from the second bed. During the second stage of the pressure intensifier cycle, the side of the drive cylinder which was originally pressurized is vented to ambient through the first activated bed which desorbs moisture from the bed. Simultaneously, the other side of the drive cylinder is pressurized through the second activated bed. The second activated bed dries the gas entering the drive cylinder and shuttles the pressure intensifier piston to the other side.
The foregoing and other objects of the present invention are achieved by a drying kit for retrofitting a pressure intensifier used in a pressure swing adsorption system. The pressure intensifier has a first side and a second side. The pressure swing adsorption system has a pair of molecular sieve beds and a first valve connected to a source of pressurized gas and to one of the pair of molecular sieve beds and a second valve connected to the source of pressurized gas and to the other of the pair of molecular sieve beds. The drying kit includes a first activated bed connectable to the source of pressurized gas and to the first side of the pressure intensifier and a second activated bed connectable to the source of pressurized gas and to the second side of the pressure intensifier. At least one valve is provided to selectively connect said first activated bed to the source of pressurized gas and to selectively connect the second activated bed to the source of pressurized gas.
The foregoing and other objects of the present invention are achieved by a pressure swing adsorption system having a pressure intensifier including a drying apparatus. The pressure swing adsorption system includes a pair of beds having molecular sieve material each having an inlet and an outlet. A pneumatic drive cylinder has opposed sides which are alternatively pressurized in order to drive the pressure intensifier. The pair of beds are coupled to a source of compressed feed air. The pair of moisture removing beds are each connected to the source of compressed feed air. The pressure intensifier is alternatively pressurized with feed air via the pair of moisture removing beds. At least one valve is located between the source of compressed feed air and the pair of moisture removing beds.
The present invention provides a method and apparatus for drying drive gas before it enters the drive cylinder. The present invention includes two beds of activated alumina or similar material, which can remove moisture during a PSA cycle. One bed is placed in series in each drive gas line for the pressure intensifier or boost pump. The beds are sized such that there is sufficient material to adsorb the moisture contained in the volume of gas required to move the drive piston through a complete stroke. During operation as one side of the cylinder is pressurized the gas entering the cylinder is dried by the activated alumina bed. The gas from the other side of the piston is vented back to ambient through the other bed which regenerates the activated alumina in that bed due to the desorption caused by the drop in pressure. The present invention is usable as a drying apparatus for a pressure intensifier in a pneumatic circuit for a conventional PSA system. The present invention is also usable as a drying apparatus for a pressure intensifier in a pneumatic circuit for a system utilizing the gas conservation scheme described in U.S. Pat. No. 5,354,361. Advantageously, activated beds can be incorporated into the drive cylinder body or the drive caps to eliminate extra components and minimize weight and size. The present invention can also be provided as a kit to retrofit a drying apparatus to an existing pressure swing adsorption system having a pressure intensifier.
It is still another object of the present invention to provide a pressure swing adsorber and a pneumatically driven booster in which the timing of the valves which control the operation of the concentrator and the booster, and the plumbing between the concentrator and the booster are selected to control the timing of the transfer of gases which are admitted to the sieve beds.
Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature and not as restrictive.